The subject of the present invention is a belt for sealing the discharge device of a bottom-pouring ferrous-metallurgical vessel and/or the device for bringing into position and for exchanging a pouring tube, comprising a top or reference plate applied from below and a fixed bottom plate carrying the pouring tube.
The invention finds wide application in the manufacture of refractory elements of a device for changing a pouring tube or of a closing-off device having sliding plates for a metallurgical vessel from which the steel is discharged into a mold or an ingot mold.
It is known that the tap hole of a closing-off device having plates which can slide or are simply superimposed is at a reduced pressure compared to the ambient atmosphere. This reduced pressure causes an intake of ambient air, especially in the region of the joint between the refractory plates and through possible cracks in said plates. This air intake turns out to be highly detrimental both to the quality of the metal poured and to the behavior of the elements made of refractory material. Oxygen, nitrogen and moisture contained in the air taken into the runner react chemically by oxidation, nitriding and/or hydriding to the detriment of the liquid metal as well as to the detriment of the elements made of refractory material.
Air mechanically entrained during pouring causes metal to rise back up or exogenous blowholes to be formed. Furthermore, the oxidized metal tends to stick in the pouring tube and to give an oxide film which, in the case of an ingot mold, can initiate skin defects.
Various attempts have been made to prevent air infiltration into the tap hole through the junction zone between the reference plate (top plate) and the plate which carries the pouring tube (bottom plate). They are based on the idea of creating, around the unsealed parts of the tap hole, an artificial atmosphere consisting of an inert gas, such as argon for example, so that the gas taken in does not cause a detrimental effect.
Document FR-A-2,227,073 describes a closing-off device having sliding plates, in which device the lower face of the reference plate which forms the sliding surface, has a single groove extending in the form of a U around the tap hole. The groove is connected to an inert-gas source. The ends of the branches of the U are separated by a distance greater than the diameter of the tap hole. This groove makes it possible to develop, in the pores of the refractory materials which surround the tap hole, a gas pressure which opposes the ferrostatic pressure and prevents the steel from wetting the refractory materials.
Finally, a method is known, from Belgian Patent No. 891,379, for rendering airtight a device for closing off the orifice for bottom discharge of a metallurgical vessel comprising a reference plate made of refractory material. A substantially circular groove, forming a sealed lock around the tap hole, is formed in the lower face of the reference plate. The groove is isolated by an inner annular sealing zone and an outer annular sealing zone, these zones being concentric, formed in at least one of the contact faces of the two plates which are perfectly applied one against the other. It is connected to an inert-gas source.
The main drawback of the single groove resides in the fact that the resulting safety is insufficient. The preventive measure constitutes only a single precaution. Furthermore, it allows no control or detection of a possible anomaly.